The invention relates to a gas discharge lamp with at least one capacitive coupling structure.
Gas discharge lamps of this kind are usually formed by a discharge vessel with two ceramic electrodes which are fused into the vessel. A discharge gas is present inside the vessel. Various operational modes are known for exciting a gas discharge through the emission of electrons.
In addition to the generation of the electrons at so-called hot electrodes by means of glow emission, the gas discharge may alternatively be generated through the emission of electrons in a strong electric field, or directly through ion bombardment (ion-induced secondary emission). In a capacitive operational mode, capacitive coupling structures are used as the electrodes. These electrodes are formed from a dielectric material which is in contact with the discharge gas at one side and which is connected to an external current circuit with electrical conduction at the other side. An AC electric field is generated in the discharge vessel by means of an AC voltage applied to the electrodes, in which field the electrons move and excite a gas discharge in a known manner.
A gas discharge lamp operating by this principle is known from DE 199 15 616.6, in which the coupling structures are formed by a ferroelectric ceramic material. The ceramic material is formed by Ba(Ti1-xZrx)O3 with dopants of donor/acceptor combinations, a preferred value being chosen to be x=0.09. A high value of the dielectric constant and of the remanent polarization can be achieved with such a ceramic material.
It is an object of the invention to provide a gas discharge lamp of the kind mentioned in the opening paragraph whose operational properties are further improved, in particular as regards the luminous efficacy.
Furthermore, a gas discharge lamp is to be provided which can operate at higher operational temperatures as compared with the cited prior art.
This object is achieved with a gas discharge lamp having at least one capacitive coupling structure in that the coupling structure comprises a ceramic material which comprises pure BaTiO3. The word xe2x80x9cpurexe2x80x9d in this connection should be understood to relate to BaTiO3 which is not doped and comprises no zirconium.
A particular advantage of this solution lies in the fact that the operating temperature of gas discharge lamps with this ceramic material may be higher than 100xc2x0 C., whereas it is limited to approximately 80xc2x0 C. in the prior art cited above.
The dependent claims relate to advantageous further embodiments of the invention.
The Curie temperature of the ceramic material can be raised to above 130xc2x0 C. with the embodiments as claimed in claims 2 and 7.
A coercitive field strength of less than 80 V/mm and a saturation polarization of at least 17 xcexcC/cm2 can be achieved in particular with the embodiments as claimed in claims 3 to 5.
The embodiment of claim 6 is offered for reasons of the simple manufacture of its material.